NO155935B - R'3 SINH-CONTAINING SILAZAN POLYMES AND PROCEDURES FOR PREPARING THEREOF. - Google Patents

Description

Method for partial dehalogenation of di- and resp. or trihaloacetic acid.

In the production of monochloroacetic acid, e.g. by direct chlorination of acetic acid, it occurs as by-products such as known di- and trichloroacetic acid. The formation of these by-products can be kept within certain limits, for example in the continuous technical production of monochloroacetic acid by continuously removing approx. 10 to 15 percent of the chlorination liquid (the "circulation liquid") from the circuit. This liquid, which besides di- and trichloroacetic acid also contains monochloroacetic acid and unreacted acetic acid, can be completely converted to trichloroacetic acid by chlorination, of which then e.g. the corresponding sodium salt can be prepared. However, as the need for trichloroacetic acid is relatively small, the main amount of the aforementioned liquid is a waste product that must be discarded.

In the German patent no. 910 778 it is

already shown a way to work up the worthless chlorination liquid into a useful liquid by passing it in a vapor state at a temperature of 180° — 250°C in the presence of hydrogen over a suitable hydrogenation catalyst. Thereby, the mixture is practically completely transferred into acetic acid, which is very useful. Apart from the fact that the need for acetic acid can be met

otherwise, this method has the disadvantage that the catalyst used becomes inactive already after approx. 14 days operating time due to strong resin formation.

It must then be regenerated by burning off the polymerization products that cause the resin formation. In terms of experience, this regeneration can only be carried out once or twice, as the resin formation has then progressed to such an extent that the catalyst is completely destroyed during burning, so that the relatively expensive precious metal catalyst only has a short life.

A more gentle method with regard to catalyst wear for transferring the chlorination liquid into a technically valuable product is described in German patent no. 1 072 980, which relates to the production of monohaloacetic acid by partial dehalogenation of di- and resp. or trihaloacetic acid, i.e. a mixture which is identical to the aforementioned chlorination liquid. The procedure essentially consists in partially dehalogenating di- and resp. or trihaloacetic acid by transfer in the vapor state together with hydrogen over a hydrogenation catalyst at a temperature between 60 and 140°C. Do you then work in

the range from 100°C to 140°C, then occurs

predominantly monohaloacetic acid, while in the temperature range from 60°C to 100°C the formation of dihaloacetic acid predominates.

In order to ensure a sufficient at the relatively low dehalogenation temperatures

reaction, it is necessary to supply the vapors developed from the chlorination liquid as quickly as possible to the catalyst, which

is effected by means of an inert carrier gas or with the hydrogen used for hydration. The required gas resp. amount of hydrogen amounts to approx. 30 times the amount of hydrogen theoretically required for dehalogenation.

By carrying out this method, it has now been shown that the use of an inert carrier gas or of hydrogen in the mentioned quantities is technically unfortunate and particularly uneconomic as the reaction components participating in the dehalogenation reaction in a too diluted state pass over of the catalyst so that the quantity passed through a single transfer of the gas over the catalyst is too small, and thereby the separation of the reaction products formed in a highly diluted state presents great difficulties. Furthermore, it cannot be avoided that parts of the formed reaction products, especially those with a relatively high partial pressure, such as e.g. acetic acid or especially hydrogen chloride is incompletely secreted and thus escapes outwards with the carrier gas. Finally, when the hydrogen chloride contained in the carrier gas is highly diluted, when the gas is washed out with water, it only gives an acid of low concentration, which may have to be concentrated.

It has now surprisingly been found that the disadvantages of the above-mentioned methods can be overcome, especially in the method according to German patent no. 1 072 980, and the use of large amounts of a carrier gas can be dispensed with when carrying the halogenoacetic acids resp. the chlorination liquid to be hydrogenated, in finely divided droplet form as a mist, together with hydrogen over the catalyst.

The invention therefore relates to a method for partial dehalogenation of di- and resp. or trihaloacetic acid by transfer of di- and resp. or trihaloacetic acid or a corresponding solution of these acids, in particular a mixture that occurs as a by-product of the halogenation of acetic acid to monohaloacetic acid and which is referred to as circulation liquid, together with hydrogen over a hydration catalyst, which is applied to a carrier, the method being characterized by ! atomizes the preheated starting product by means of an excess of hydrogen or a mixture of hydrogen and an inert gas into a fine liquid mist and passes the latter in mixture with hydrogen through a catalyst furnace filled with a hydrogenation catalyst, where a temperature of 60° — 140°C is maintained, whereupon by means of cooling, the reaction mixture emerging from the contact furnace is separated in a subsequent separator into liquid, dehalogenated product on the one hand and gaseous components on the other side, which are removed over the head of the separator.

For atomization of the starting product, which is advantageously preheated in advance to the prevailing temperature in the catalyst furnace, a nozzle is suitably used with the help of which the starting material is either atomized by means of a hydrogen stream or a mixture of hydrogen and an inert gas, such as e.g. nitrogen or carbon dioxide and the like, into the catalyst - the furnace. The liquid mist flowing out of the nozzle, which is mixed with hydrogen, is dehalogenated by brushing over the catalyst so that the dehalogenated mixture emerges from the catalyst - furnace together with the hydrogen halide and excess hydrogen resp. inert gas. For dehalogenation, the known hydrogenation catalysts are suitable, such as e.g. the metals from the 8th group of the periodic system, preferably the metals of the platinum group, individually or in a mixture, resp. as an alloy, as these metals are used in the form of their salts applied to a suitable carrier. The dehalogenation process itself can be carried out under atmospheric pressure or under reduced pressure, working in a vacuum, for example under a pressure between approx. 20 mm Hg to below atmospheric pressure, has a beneficial effect on the colorlessness of the process product formed.

The reaction band emerging from the catalyst furnace is separated in subsequent separators after previous cooling into liquid and gaseous components, the latter being removed at the top and subjected to a renewed stepwise post-cooling, for example at a temperature between approx. +50° and +3°C. The liquid components of the reaction mixture formed in the separator consist predominantly of the monohaloacetic acid, which contains smaller amounts of dihaloacetic acid, acetic acid and hydrogen chloride. From the gases removed from the separator, the hydrogen halide can be removed by means of water washing, so that the remaining residual gas is available for renewed use in the catalyst furnace or to the atomization of the starting product.

An exemplary embodiment of the method according to the invention is shown in the drawing, where 1 indicates a storage vessel from which the output product to be heated, via line 2, after previous heating in the heater 3, is supplied to the catalyst furnace by means of atomization.

The starting product is atomized using a nozzle 5 using hydrogen which flows to the nozzle 5 via line 6. In the catalyst furnace 4, a temperature of 60° to 140°C is maintained. The di- and trihaloacetic acid contained in the starting product is almost completely dehalogenated to monohaloacetic acid by passing through the catalyst in the presence of hydrogen during hydrogen halide formation. The liquid mist and vapors escaping from the catalyst furnace 4 come via line 7 while simultaneously cooling in the cooler 8 to the separator 9, in which the liquid monohaloacetic acid collects and can be taken out via line 10. Above the top of the separator 9, the gaseous components of the reaction mixture are removed via line 11 and is further cooled step by step for post-condensation in a cooling unit 12, possibly with a solar cooler. 14 over line 15. Corresponding to the amount of washing water used, a halogenated hydrogen acid of the desired concentration can be withdrawn at the bottom of the washing tower 14 over line 16. The hydrogen halide-purified exhaust gas, which also contains excess hydrogen and possibly inert gas, is removed from the washing tower 14 via line 17 and, after previous drying, is led via line 6 again, together with fresh hydrogen into the catalyst furnace 4.

The method according to the invention has the advantage compared to the known working methods! with the starting product's good dosability, as well as the fact that large quantities of a carrier gas are not used, whereby the loss of formed reaction products is avoided. Furthermore, the space-time yield is increased, and by working in the liquid phase, overheating and resin formation on the catalyst is avoided. Finally, special solvent additions to the starting product are made redundant, as is common when working in the gas phase, and the hydrogen halide formed as a by-product can be transferred without special precautions into a corresponding acid of the desired concentration.

Example 1.

In the catalyst furnace containing 1000 ml or 390 g of granular silica gel, on which 8 g of palladium chloride had been applied as a catalyst, it was per hour using 75 ml hydrogen injected 250 g starting material with composition: 40.4% monochloroacetic acid 54.8% dichloroacetic acid

1.0%: trichloroacetic acid 3.6% acetic acid 0.1% hydrogen chloride.

In the catalyst furnace, a temperature of 114-118°C was maintained. The work was carried out at normal pressure. The final product formed in the separator had the following composition:

89.6 percent monochloroacetic acid

4.6% dichloroacetic acid 5.6% acetic acid 0.1% hydrogen chloride.

The yield of the final product and the hydrogen chloride contained in the concentrated hydrochloric acid, calculated on the starting material used and the hydrogen consumed, amounted to 98.8 per cent.

Example 2.

In the catalyst furnace containing 1000 ml of the catalyst used in example 1, with the help of 50 ml of hydrogen per hour injected 250 g starting material of composition: 62.4 percent dichloroacetic acid 27.6 percent monochloroacetic acid

1.2% trichloroacetic acid 9.1% acetic acid 0.1% hydrogen chloride.

In the catalyst furnace, a temperature of 116°-117°C and a pressure of 300 mm Hg were maintained. The final product formed in the separator had the following composition:

84.7 percent monochloroacetic acid

5.3% dichloroacetic acid 9.7% acetic acid 0.1% hydrogen chloride.

The yield of the final product and the hydrogen chloride contained in the concentrated hydrochloric acid calculated on the starting material used and the hydrogen consumed amounted to 99.3 per cent.

Example 3.

Into the catalyst furnace, which contains 1000 ml of the catalyst used therein in example 1, was per hour using 35 liters of hydrogen inject 250 g of a chloroacetic acid mixture of composition formed by chlorination of acetic acid

25.6% monochloroacetic acid 34.2% dichloroacetic acid 34.8% trichloroacetic acid

5.0 percent acetic acid.

The temperature in the catalyst furnace was 70°C. The work was done at atmospheric pressure. The final product formed in the separator had the following composition: 28.4 percent monochloroacetic acid

61.3% dichloroacetic acid 4.1% trichloroacetic acid 5.6% acetic acid.

The yield of the final product and the hydrogen chloride contained in the concentrated hydrochloric acid, calculated on the starting material used and the hydrogen consumed, amounted to 98.1 per cent.

Example 4.

It was per hour injected 300 g of a bromo-acetic acid mixture formed by bromine mg of acetic acid of composition: 58.2 percent monobromoacetic acid 32.1 percent dibromoacetic acid 9.4 percent acetic acid by means of 30 liters of hydrogen under a pressure of 300 mm Hg into the catalyst furnace, which had a catalyst filling, corresponding to that indicated in example 1. In the catalyst furnace, a temperature of 80°C was maintained. The final product formed in the separator had the following composition: 89.0 percent monobromoacetic acid

0.5% dibromoacetic acid 10.1% acetic acid.

The yield of the final product of formed hydrogen bromide, calculated on the material used and the hydrogen consumed, was 98.3 per cent.

Claims (2)

1. Method for partial dehalogenation of di- and resp. or trihaloacetic acid in that di- and resp. or trihaloacetic acid or a corresponding solution of these acids, in particular a mixture formed by the halogenation of acetic acid to monohaloacetic acid as a by-product and designated as "circulation liquid", is preheated and passed together with hydrogen over a hydration catalyst that is applied to a carrier, at an elevated temperature, characterized by atomizing the preheated starting product using an excess of hydrogen or a mixture of hydrogen and an inert gas into a fine liquid mist and passing the latter through a catalyst furnace filled with a hydrogenation catalyst, where a temperature of 60° — 140°C is maintained, after which the reaction mixture emerging from the catalyst furnace is separated by cooling in a subsequent separator, on the one hand into liquid dihalogenated product and on the other hand into gaseous components which are removed over the top of the separator. 2. Process according to claim 1, characterized in that the starting product is fed at a pressure below atmospheric pressure, but above 20 mm pressure above the catalyst.